Bats, diseases, and the Ebola epidemic
After discussing in length about how wonderful bats are for our agriculture and for our forests, in my last post, I hinted at the fact that they also carry diseases that are sometimes lethal when transmitted to humans.
I specifically mentioned rabies in that post. The website maintained by Centers for Disease Controls and Prevention tells us that contact with bats is the most common way by which people get rabies in the United States. The same article begins by saying “Most bats don’t have rabies.” It also mentions that among bats that are tested for rabies (after suspicious symptoms are observed), only 6% are found to have the virus.
But rabies is not the only one
Commenting on my last post, @mountainwashere mentioned that bats have also been known to be natural reservoirs for Nipah and Hendra viruses. A natural reservoir is an organism which acts as a host for a disease-causing parasite without getting sick itself.
Bats have been found to act as reservoirs for an astonishing array of viruses dangrous for human beings. In a 2006 article focusing on this topic, the authors discuss 66 different viruses isolated from or detected in bats.
These words appear in the abstract of the same article:
“It is clear that we do not know enough about bat biology; we are doing too little in terms of bat conservation; and there remain a multitude of questions regarding the role of bats in disease emergence.”
And the bats are scary again
The authors of that study appear worried about indiscriminate killing of bats fueled by the new discoveries relating bats with emerging viruses. Similarly, the authors of a 2003 article on Brazilian bats express concern about how vaccination against exposed livestock was not being made a priority, but bats were being killed indiscriminately.
In order to have a clearer picture of this process of transmission from bats followed by destruction of bats, let us look at a recent outbreak of a virus that has also been linked to bats.
Then comes Ebola
In December 2013, a mysterious disease started spreading in the West African country of Guinea and it remained mysterious until it was identified in March 2014. It was identified as the Ebola virus which causes fever, headache, fatigue, diarrhea, vomiting, stomach pain, and if left untreated, death. It quickly spread to other countries in Africa and around the world. Finallly, on January 13, 2016, the World Health Organization declared that Liberia, the last of the country affected, was Ebola-free.
In about two years, 11,315 people had died from infections in Guinea, Sierra Leone, Liberia, Nigeria, Mali, and the United States.
The ebola cycle
Image is in the public domain.
Unpredictable outbreaks of Ebola had been reported since 1976, but this was the biggest epidemic of the virus resulting in the largest number of reported cases and deaths. Scientists had been puzzling over the source of this virus for a long time. Many animals, including antelopes, chimpanzees, and gorillas were found to contract the virus and die. Humans could get the virus by touching or eating these dead or infected animals, but the problem was scientists had not been able to find any living organism carrying the virus.
And the answer was bats
Bats are presumptive reservoirs for Ebola because antibodies that fight against the Ebola virus have been detected in bats. This means that some species of bats can survive when infected with the ebola virus. An antibody is a cell used by the body to fight against bacteria or viruses. So if an antibody against a certain virus is found in an animal body, we can assume that the animal has previously been infected by that disease and has survived that attack. That is the principle on which vaccinations work.
A little detour into antibodies
For example, the vaccine for the smallpox virus, which has saved billions of lives, introduces a similar but less dangerous cowpox virus into the body. The body creates antibodies that fight the cowpox disease, and these antibodies will stay in the system and will also fight the smallpox virus. So if we tested an immunized person and found the antibodies against cowpox, we could say that the person had been infected by cowpox and had survived it, and we would be correct.
To be completely accurate, modern versions of the smallpox vaccine use a different virus that is related to both the cowpox virus and the smallpox virus. Edward Jenner, who pioneered the vaccine, used the cowpox virus (or the smallpox of the cow). Because of this, the word “vaccine” is itself derived from the Latin word for cow.
Back to Ebola
In order to determine where the Ebola outbreak started, a group of scientists conducted a retrospective case study. They used “surveys, interviews, and molecular analyses of bat and environmental samples” that led them to a case involving a 2-year old boy in a remote village called Meliandou in Guinea. The boy had got sick and died within a few days followed by his family members followed by the people who went to their funerals and the epidemic had spread across the country and the world. The scientists then tried to figure out how the boy could have contracted the disease.
Their analysis led them to a hollow tree with a roost of bats where the boy had been known to play. The insectivorous free‐tailed bats (Mops condylurus) had previously been found to be resistant to the virus infection and the researchers believed that the boy had come in contact with the bats and thus contracted the disease. When the researchers reached the village to study the bat colony, the tree had been burned and there was only a stump present. The villagers said there had been a rain of bats as the fire engulfed the colony along with the tree.
The village of Meliandou is located in what is called the Forest Region of Guinea. A WHO report on the origins of the 2014 Ebola outbreak mentions how that name is ironic because 80% of the forest in the region has been destroyed by foreign mining and timber operations. The same article mentions that this could have caused the wild animals to come into contact with humans leading to the transmission of the virus.
Answers are not final
More recently,researchers found that Ebola was more widespread than suspected, and that several more species along with the bats could be potential carriers of the virus. One of the researchers quoted in that article says, “We don’t want people to be alarmed that there are so many different species, and start killing as many as possible.”
As always, the picture is quite complex. Bats do carry harmful viruses, but we certainly do not want to destroy them. That would leave us with unpleasant consequences in our agriculture and forests and insect populations. So the best way out is to learn the art of peaceful coexistence, and to help conserve their natural habitat.
Having said that, please get medical attention if you are bitten by a bat. This page has information on what to do in case you (or your pet) come in contact with one.
Links to references and image sources are provided in the text.